MathDB
Vietnam TST #5

Source: Vietnam TST 2022 P5

April 27, 2022
base systemcombinatorics

Problem Statement

A fractional number xx is called pretty if it has finite expression in baseb-b numeral system, bb is a positive integer in [2;2022][2;2022]. Prove that there exists finite positive integers n4n\geq 4 that with every mm in (2n3;n)(\frac{2n}{3}; n) then there is at least one pretty number between mnm\frac{m}{n-m} and nmm\frac{n-m}{m}